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Vocoder Pitch Smoothing

IP.com Disclosure Number: IPCOM000094917D
Original Publication Date: 1965-Jul-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 28K

Publishing Venue

IBM

Related People

Bandat, K: AUTHOR [+5]

Abstract

Pulse-excited vocoder systems which utilize an excitation function derived from the glottal period in the speech signal can be unduly sensitive to noise in that signal. Such noise can result in spurious indications of change in the period length, with consequent erroneous reconstruction of the speech signal. One way of overcoming this is to smooth the excitation function in accordance with a rule which minimizes disturbances introduced by noise.

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Vocoder Pitch Smoothing

Pulse-excited vocoder systems which utilize an excitation function derived from the glottal period in the speech signal can be unduly sensitive to noise in that signal. Such noise can result in spurious indications of change in the period length, with consequent erroneous reconstruction of the speech signal. One way of overcoming this is to smooth the excitation function in accordance with a rule which minimizes disturbances introduced by noise.

Speech signal SPS is first split up among a number of spectrum channels SPC and excitation channel EC. Signal SPS is supplied via line 10 to discriminator D, for determining whether such is voiced or unvoiced, and via line 12 to glottal pulse period detection circuitry 14. Circuitry 14 includes non-linear member NL, bandpass filter BP. polarized zero-crossing detector ZC, and pulse shaper PS. The output of PS supplies a defined square pulse for each zero- crossing in one direction. This is indicative not only of the true pulse period but also certain noise content in the input speech signal. Gate G1 is conditioned, via line 16. to pass the output of PS during the time the speech signal is voiced. Gate G2, on the other hand, applies the square pulses of the excitation function during the unvoiced portions of the speech signal directly via line 18 to EC. The excitation pulses passed from PS by G1 are first applied to device I for measuring the period length of the excitation pulses and subsequently s...